antibodybinding

Antibody binding refers to the specific non-covalent interaction between an antibody and an antigen, typically between the antibody's variable regions and a particular epitope on the antigen. This binding drives immune recognition and is central to many diagnostic and therapeutic techniques.

Specificity and affinity: The antigen-binding site, or paratope, recognizes a defined epitope. Affinity describes the strength of a single binding event and is commonly quantified by the equilibrium dissociation constant (KD); lower KD means tighter binding. Avidity describes the overall binding strength of a multivalent antibody to multivalent antigens.

Structural basis: Most antibodies have two antigen-binding sites, enabling potential bivalent engagement. Epitopes may be linear or conformational. The complementarity-determining regions within the antibody's variable domains determine specificity and binding geometry, while the Fc region mediates effector functions rather than direct antigen contact.

Kinetics and environment: Binding is governed by rates of association (kon) and dissociation (koff); KD = koff/kon. Binding strength is influenced by temperature, pH, ionic strength, and antigen presentation. Cross-reactivity occurs when a single antibody binds related epitopes, which can be desirable or problematic.

Measurement and applications: Binding is assessed by assays such as ELISA, Western blot, immunohistochemistry, surface plasmon resonance, and bio-layer interferometry. Antibody binding underpins vaccines, therapeutic antibodies, diagnostic tests, and research tools, and is a focus of antibody engineering and affinity maturation.